1. Field
The invention is in the field of foot prostheses which attach to an amputation socket and provide an artificial leg and foot for a wearer.
2. State of the Art
There are a number of different foot and leg prosthetic devices currently in use. The primary goal of these devices is to extend an amputated leg stump to the ground so as to support the wearer while upright and enable him to walk. The earliest prior art was merely a peg secured to the amputated limb which provided minimal mobility to the wearer. Later, a foot was added to the bottom of the peg.
Most prior art feet were constructed as either a single foot piece attached to a shank strut or a heel segment attached to a continuous shank and forefoot segment. An example of a more modern basic foot prosthesis is known as the "SACH" Foot, "SACH" standing for Solid Ankle Cushioned Heel. The "SACH" foot is a carved wooden foot with an aluminum leg strut for attaching the foot to the amputation socket. Additional improvements made to the basic device by way of ankle hinges or ball joints improved mobility. However, due to the rigidity and weight of the components, including the mechanical joints, such prostheses remained unnaturally heavy and stiff.
Recent improvements to foot prosthesis configurations utilize modern composite material technology to impart energy storage and release during use. Examples of these are the so called "Seattle Foot", which is a molded plastic foot, and the prosthesis shown in U.S. Pat. No. 4,547,913, known as the Flex-Foot, which provides a composite strut and foot configuration. The spring-like action imparted by the materials used results in additional mobility and comfort to the wearer. However, such prior art retains certain design characteristics which prohibit the use of inexpensive and lightweight fiberglass composite materials.
All known devices within this group are made up of individual components that must be fastened together, be it a separate sole or heel member to a foot member or a separate foot member to a connection leg extension strut member. These joints must be rigidly constructed so as to be strong enough to withstand the concentrated loads transmitted through them. The result is that local stiffness occurs, which interferes with smooth and even flexing of the components during the wearer's stride. Even with rigidly constructed joints, these devices are prone to fatigue and fracture at the joints, thus placing the wearer at risk of injury.
In addition, composite materials exhibit poor bearing strength where fasteners penetrate the construction. The accumulated wear and erosion of structural material surrounding fasteners result in loss of position or support of attached components after a period of continual use. The fastening of the heel to the ankle portion of the foot as in U.S. Pat. No. 4,547,913, occurs at the highly stressed ankle zone. To prevent fracture, the buildup of materials required for strength makes attractive cosmetic finishing of the ankle area difficult. Providing a structurally adequate, yet lightweight, cosmetically pleasing, and inexpensive ankle has long remained a problem.
Furthermore, while substantially lighter in weight and more natural in flexibility, the components of this type of prosthesis are generally significantly costlier than the prior art "SACH" type devices. It has long been desired to be able to use low priced, lightweight materials, such as fiberglass composite materials. However, the available inexpensive fiberglass composite materials lack the needed strength required for use in the prior art designs. By the term "fiberglass composite materials", it is to be understood that materials such as commercial grade, E-glass.RTM., unidirectional and/or cross-plied fabrics embedded in resins, such as wet laminating epoxy resins and orthothalic and/or isothalic polyester resin matrix material, are intended.